In a paper conveying apparatus of an image reading apparatus, image copying apparatus, etc., sometimes a jam occurs when the paper moves along the conveyance path. In general, a paper conveying apparatus is provided with the function of determining whether a jam has occurred by a paper being conveyed to a predetermined position inside the conveyance path within a predetermined time from the start of conveyance of the paper and of stopping the operation of the apparatus when a jam has occurred.
On the other hand, if a jam occurs, a large sound is generated in the conveyance path, so the paper conveying apparatus can determine whether a jam has occurred based on the sound which is generated on the conveyance path and thereby detect the occurrence of a jam without waiting for the elapse of the predetermined time.
A detection apparatus of printed matter which determines that a bill is normal if the level of an output signal of a filter which passes only a signal of a frequency band which is set in advance according to the type of the paper currency is higher than a preset detection level and determines that a bill is damaged if the level is lower than that, has previously been disclosed (see Japanese Laid-Open Patent Publication No. 61-169983).